It is known in the prior art to use electric arc welding to weld radiator core tubes to a header, which header has apertures for engaging tube ends that protrude therethrough.
In the prior art, the welding apparatus traces around the entire perimeter of a generally oval welding joint formed by protruding an oval shaped tube end through an aperture in the header. The tube ends form a generally rectangular array of oval welding joints, and the prior art welding apparatus under various combinations of automated control and manual intervention positions the tip of the welding head at a starting point on the oval, strikes an arc, and then traces a circuit all the way around the oval tube end to complete the weld. The welding head is then moved on to the next oval and the cycle is repeated. It is typical to carry out the welding process in a tungsten inert gas (TIG) environment.
Such prior art trace welding can be a problem in that porous and therefore weak welds prone to leakage can result therefrom. Cartridge brass, which is about 70% copper and 30% zinc, is typically used to form both the header and the tubes. Because the welding temperatures resulting from the trace welding operation can be in the neighborhood of 10,000.degree. F., a relatively high heat input is applied to the joint. The zinc tends to boil out and leave a rather porous copper, which results in a weak joint. Therefore, back filling the joints with solder to strengthen the bond is often necessary. Even so, when the radiator core is subjected to the thermal, pressure, and mechanical stresses of use in a vehicular engine, leaks and failures can occur at an undesirable rate.
Additionally, the trace welding technique can be tedious and inefficient, one reason being because each oval must be traced one at a time and the welding head must be properly cued up for each oval, one at a time. Depending upon the sophistication of the operator, whether it be manual or computer driven, any lack of uniformity in the shape and size of the ovals can lead to welding head misalignment and less than optimum welded joints. Increased accuracy comes at the cost of reduced speed.
Prior art trace welding machines, because of the required precision and relatively low permissible margin for error, can be quite costly. Even so, such machines often produce welded radiator cores at a relatively slow rate, which cores then may need backfilling, a further cost disadvantage.
U.S. Pat. Nos. 4,425,491; 4,319,113; and 3,675,841 show a variety of apparatus and methods for carrying out welding operations such as for example continuous welding of a series of tubes to a tube sheet.
The art also shows arc welding ferromagnetic workpieces under the control of a magnetic field, which can be used to move the arc. See, e.g., U.S. Pat. No. 4,443,686; 4,246,464; 4,278,868; 4,511,784; and 3,626,145.